Some rate and modeling studies on the use of iron--titanium hydride as an energy storage medium for electric utility companies

Dynamic tests and modeling studies were made on the chemical-energy-storage portion of an electrical energy conversion and storage system proposed for leveling the load of an electric utility company. The concept utilizes off-peak power to produce hydrogen by electrolyzing water, storing the hydrogen as iron-titanium hydride, FeTiH/sub x/, and subsequently releasing the hydrogen to a fuel cell where the reaction with air generates electrical power. The hydrogen storage portion of the system was tested on a small scale using a 6-in.-diam by 30-in.-long test bed containing 84 lb of FeTi alloy. Hydrogen reacts with this alloy at ordinary temperatures, with the release of heat, producing the hydride FeTiH/sub x/; and hydrogen is released by heating the hydride to decompose it. In the six hydriding-dehydriding cycles that were studied, the times that hydrogen flow rates of 40 to 10 standard liters per minute (SLPM) could be sustained were determined. Water temperatures of 30/sup 0/C and 50/sup 0/C were used; and the terminal hydrogen pressures used were 500 psia during hydriding and about 16 psia during dehydriding. Under these conditions the dynamic working capacity of the test bed was 1 lb of hydrogen as the composition varied between FeTiH/sub 0.175/ and FeTiH/sub 1.400/. For a 10-h transfer time the design rating of the unit was 9 SLPM of hydrogen, which is equivalent to 0.119 wt% of the alloy per hour, using water at 80/sup 0/C. Temperature profiles and histories were also obtained. A battery comparison test showed that the reserve capacity of the test bed was substantially greater than that expected from the best present-day lead-acid battery in a standard test made at the 50%-discharged condition. In the modeling study it was shown that by using measured values of the bed thermal conductivity and pressure, the analytical and experimental results for hydrogen discharge rate, and amount of hydrogen discharged, were in good agreement.